class Base64 {
  private keyStr:string = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
  private utf8_encode (string: string) {
    const str = string.replace(/\r\n/g,"\n");
    let utftext = ""
    for (let n = 0; n < str.length; n++) {
      const c = str.charCodeAt(n)
      if (c < 128) {
        utftext += String.fromCharCode(c);
      } else if((c > 127) && (c < 2048)) {
        utftext += String.fromCharCode((c >> 6) | 192);
        utftext += String.fromCharCode((c & 63) | 128);
      } else {
        utftext += String.fromCharCode((c >> 12) | 224);
        utftext += String.fromCharCode(((c >> 6) & 63) | 128);
        utftext += String.fromCharCode((c & 63) | 128);
      }
    }
    return utftext
  }
  private utf8_decode (utftext: string) {
    let string = "";
    let i = 0;
    let c = 0;
    let c3 = 0;
    let c2 = 0;
    while (i < utftext.length) {
      c = utftext.charCodeAt(i)
      if (c < 128) {
        string += String.fromCharCode(c)
        i++
      } else if ((c > 191) && (c < 224) ) {
        c2 = utftext.charCodeAt(i+1)
        string += String.fromCharCode(((c & 31) << 6) | (c2 & 63))
        i += 2
      } else {
        c2 = utftext.charCodeAt(i+1);
        c3 = utftext.charCodeAt(i+2);
        string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
        i += 3;
      }
    }
    return string
  }
  // 加密
  public encode (input: string) {
    let output = ""
    let chr1, chr2, chr3, enc1, enc2, enc3, enc4
    let i = 0
    input = this.utf8_encode(input);
    while (i < input.length) {
      chr1 = input.charCodeAt(i++);
      chr2 = input.charCodeAt(i++);
      chr3 = input.charCodeAt(i++);
      enc1 = chr1 >> 2;
      enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
      enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
      enc4 = chr3 & 63;
      if (isNaN(chr2)) {
        enc3 = enc4 = 64;
      } else if (isNaN(chr3)) {
        enc4 = 64;
      }
      output = output + this.keyStr.charAt(enc1) + this.keyStr.charAt(enc2) + this.keyStr.charAt(enc3) + this.keyStr.charAt(enc4)
    }
    return output
  }
  // 解密
  public decode (input: string) {
    let output = ""
    let chr1, chr2, chr3, enc1, enc2, enc3, enc4
    let i = 0
    const inp = input.replace(/[^A-Za-z0-9+/=]/g, "")
    while ( i < inp.length) {
      enc1 = this.keyStr.indexOf(inp.charAt(i++));
      enc2 = this.keyStr.indexOf(inp.charAt(i++));
      enc3 = this.keyStr.indexOf(inp.charAt(i++));
      enc4 = this.keyStr.indexOf(inp.charAt(i++));
      chr1 = (enc1 << 2) | (enc2 >> 4);
      chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
      chr3 = ((enc3 & 3) << 6) | enc4;
      output = output + String.fromCharCode(chr1);
      if (enc3 !== 64) {
        output = output + String.fromCharCode(chr2)
      }
      if (enc4 !== 64) {
        output = output + String.fromCharCode(chr3)
      }
    }
    return this.utf8_decode(output)
  }
}
export default Base64
